diff --git a/EasyLean/Basic.lean b/EasyLean/Basic.lean
index 305e1ca..f8f73fa 100644
--- a/EasyLean/Basic.lean
+++ b/EasyLean/Basic.lean
@@ -1,12 +1 @@
-import Mathlib.Data.Real.Basic
-import Mathlib.Tactic.Linarith
-
-theorem mathd_algebra_513
-  (a b : ℝ)
-  (h₀ : 3 * a + 2 * b = 5)
-  (h₁ : a + b = 2) :
-  a = 1 ∧ b = 1 := by
-  sorry
-
-theorem eq_four : ∀ a b c d : Nat, a = b → a = d → a = c → c = b := by
-  sorry
+import EasyLean.Problems.MathdAlgebra.mathd_algebra_513
diff --git a/EasyLean/Problems/MathdAlgebra/mathd_algebra_513.lean b/EasyLean/Problems/MathdAlgebra/mathd_algebra_513.lean
new file mode 100644
index 0000000..0b0c8e2
--- /dev/null
+++ b/EasyLean/Problems/MathdAlgebra/mathd_algebra_513.lean
@@ -0,0 +1,12 @@
+import Mathlib
+
+theorem mathd_algebra_513 (a b : ℝ) (h₀ : 3 * a + 2 * b = 5) (h₁ : a + b = 2) :
+    a = 1 ∧ b = 1 := by
+  have h2 : 2 * a + 2 * b = 4 := by
+    linear_combination 2 * h₁
+  have ha : a = 1 := by
+    linear_combination h₀ - h2
+  have hb : b = 1 := by
+    have : 1 + b = 2 := by simpa [ha] using h₁
+    linarith
+  exact ⟨ha, hb⟩